This invention relates generally to rechargeable batteries and their construction. More particularly, the present invention relates to a composition for an electrode of a lithium-ion battery that has a low exothermic reaction to create a more reliable Li-ion battery.
As the term is used in electrochemistry, a battery is any of a class of devices that convert chemical energy directly into electrical energy. The mechanism by which a battery generates an electric current involves the arrangement of constituent chemicals in such a manner that electrons are released from one part of the battery and made to flow through an external circuit to another part. The part of the battery at which the electrons are released to the circuit is called the anode, or the negative electrode, and the part of the battery that receives the electrons from the circuit is known as the cathode, or the positive electrode. Some batteries, known as xe2x80x9crechargeablexe2x80x9d batteries, are constructed such that a reverse current applied to the electrodes causes the battery to recharge and hold a new capacity to discharge.
One of the most common rechargeable batteries is a lithium-ion battery. Conventional negative electrodes (or anodes) in rechargeable Li-ion batteries contain active conductive materials such as hard carbons, graphite, or MCMB, with polyvinylidene fluoride (PVDF) as a xe2x80x9cbinderxe2x80x9d material.
The electrochemical reaction in a Li-ion battery is exothermic and thus the battery generates heat in both the charge and discharge cycle. Further, significant exothermic heat generation occurs in the Li-ion battery under abusive conditions, such as a short circuit, overcharging, over-discharging, and operation at high temperatures. The exothermic heat generation is attributed to a combination of effects including the reaction of the PVDF in the electrodes with xe2x80x9clithiatedxe2x80x9d carbon, reaction of electrolyte with oxygen liberated due to decomposition of positive electrode (cathode) material, and breakdown of the electrodes passivation layers. Insufficient heat dissipation in the Li-ion battery can compromise the performance of the battery and may result in the release of combustible gasses at high temperatures, known as xe2x80x9cthermal runawayxe2x80x9d.
Accordingly, the minimization of the exothermic heat generation from the electrochemical operation of the Li-ion battery is desirable because increasing the reliability of the battery decreases the likelihood that the battery will suffer from thermal runaway and rupture. It is thus to the provision of such a battery having an electrode composition that has minimal exothermic heat generation during electrical charge and discharge of the battery that the present invention is primarily directed.